Method for initiating underground combustion



c. c. DYSON 3,417,818

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lvoooaoo.ao so @no x 7D6 0 o D O 010|'.0 0 Q 0 o oo D INVE NTOR CHARLESC. DYSON iled Jan. 9, 1967 FIGA m w Pauz. 5

CHARCOAL United States Patent O 3,417,818 METHOD FOR INITIATINGUNDERGROUND COMBUSTION Charles C. Dyson, Taft, Calif., assignor toChevron Research Company, San Francisco, Calif., a corporation ofDelaware Filed Jan. 9, 1967, Ser. No. 608,208 2 Claims. (Cl. 166-39)ABSTRACT OF THE DISCLOSURE A method of igniting underground petroleumformations having a perforated liner in the well adjacent the formationby packing the annular space between the exterior of the perforatedliner and the well wall with a combustible material, igniting thecombustible material and injecting air through the perforations of theliner to burn the combustible material and to cause the ignition of thepetroliferous material in the formation.

Briefly the present invention provides a method for igniting a petroleumbearing formation penetnated by a well and having a perforated liner inthe Well adjacent to the formation by packing the annular space betweenthe formation yand the liner with a combustible material. Thecombustible material is ignited and an oxygen containing gas is injecteddown the well and out through the perforations of the liner into thecombustible material to support the combustion thereof and to ignite thepetroleum bearing formation.

This invention relates to iguiting underground petroleum-bearingformations penetrated by a well; and, more particularly, this inventionrelates to an improved method for placing a combustion initiator in awell behind a perforated liner to elevate the temperature of anunderground hydrocarbon-bearing formation so that combustion in theformation may be started without `damage to the perforated well liner orthe well casing.

Underground combustion, wherein a portion of the oil in an oil-bearingformation is burned to assist in producing an unburned portion of theoil, has become a conventional tool of secondary recovery engineers. Oneproblem, however, that is still not completely solved concerns ignitingthe petroleum in the formation. Heretofore, ignition was accomplished ina variety of ways. However, a serious problem has been encountered whenit is ydesired to ignite cased or lined wells because the heat generatedduring ignition is often sufficient to burn out the liner or casing andcause collapse of the liner or casing possibly resulting in loss of therwell.

The present invention is directed to a method for igniting apetroliferous formation penetrated by a well and having a perforatedliner positioned adjacent the petroleum-bearing interval. In 'accordancewith the present invention, the annular space between the exterior ofthe perforated liner and the well wall is packed Ewith a combustiblematerial. At least the upper portion of the combustible material isbrought into Contact with a pyrophoric material of a type which willpermit autoignition of the combustible material in the presence ofoxygen. An oxygeneontaining gas, for example air, is then injected intothe well and ont through the perforations in the liner into thecombustible material to cause ignition to occur. The injection ofoxygen-containing :gas is continued and ignition of the entire amount ofcombustible material in the annular space is accomplished. Theoxygen-contained gas passes outward through the slots into the charcoaland then into the formation. The relatively cool gas pass- Patented Dec.24, 1968 ICC ing through the perforations prevents overheating of theliner and thus damage to the liner is avoided. In addition, the ash fromthe combustible material is Icarried into the more permeable portions ofthe oil-bearing interval and assists in reducing the iiow of gas intothese more permeable portions. This assists in redirecting air intosomewhat less permeable portions of the formation to help establish amore uniform gas injection profile which in turn results in more uniformignition and combustion in the formation.

A particular object of the present invention is to provide a method forigniting an underground formation in a manner to prevent damage to awell liner and to assist in ,assuring uniform ignition over an entirevertical interval of an oil-bearing formation.

Further objects and advantages of the present invention will becomeapparent from the following detailed description read in light of theaccompanying drawing which is made a part of this specification and inwhich:

FIGURE l is an elevational view with parts broken away for clarity ofpresentation showing the preferred form of apparatus assembled inaccordance with the present invention;

FIGURE 2 is an enlanged sectional View of a portion of the apparatus ofFIGURE l and illustrates apparatus for placing a combustible material inthe annulus between the perforated Well liner and the Well wall;

FIGURE 3 is a sectional View taken at line 3-3 of FIGURE 2;

FIGURE 4 is a sectional View showing apparatus for placing pyrophoricmaterial adjacent the upper portion of the combustible material; and

FIGURE 5 is a sectional view taken at line 5 5 of FIGURE 4.

In accordance fwith the invention, a well 20 is drilled to ahydrocarbon-bearing formation 22. A protective casing string 24 iscemented into the upper portion of the hole 20 by means of suitablecement 26. The protective casing string terminates above lthe upperportion of the hydrocarbon-bearing formation 22. The well is thendrilled through the hydrocarbon fonmation utilizing a suitablecirculating fluid, such as, for example, gas, oil, air, foam or. anemulsion. The portion of the well adjacent the hydrocarbon-formation ispreferably underreamed to a radius about two inches greater than theoutside diameter of the protective `casing string.

A perforated liner 66 is installed opposite the hydrocarbon-bearingformation. A conventional gravel packing tool, indicated generally as30, is placed in the perforated or slotted liner and is connected withthe surface by means of tubing 32. A wellhead 34 having connections forvarious fluids is located at the top of the well. Compressed air issupplied to the casing through line 36 and valve 38. Compressed inertgas is supplied to the casing through line 42 and valve 44. Acombustible material, such as charcoal, and a circulating iiuid, such asoil, are injected into the interior of pipe 32 lby means of pipe 46,pipe 48 and valves S0 and 52. The oil pipe 48 enters the charcoal pipe46 -at a suitable junction S3, preferably downstream of the charcoalcontrol valve 50.

The preferred method of placing the charcoal behind the perforated lineris shown in FIGURES 2 and 3 which is an enlarged sectional view of thelower portion of the apparatus useful in accordance with the presentinvention. The pieces of Charcoal indicated generally by the number 60,are carried by suitable circulating uid such as oil down the interior ofpipe 32. The lower portion of pipe 32 terminates in a conventionalgravel packing tool indicated generally as 30. The gravel packing tooldiverts the ow of oil and charcoal through side ports 61 and 62 into theannular space 63 between the exterior of the perforated liner and thewell wall. Packing cups 64 and 65 are adapted to direct the flow throughthe ports 61, 62.

In carrying out the method of the present invention a well is drilled toa location immediately above a hydrocarbon-bearing formation. Aprotective casing string 24 is then cemented down to the top of thehydrocarbonbearing formation 22. The well is then drilled below theprotective casing string to the bottom of the hydrocarbonbearingformation using a suitable circulating fluid such as oil, gas, air orfoam. The portion of the well penetrating the hydrocarbon-bearingformation is then widened by underreaming to a radius greater than theoutside diameter of the protective casing string located immediatelyabove the hydrocarbon-bearing formation. Preferably, the wall adjacentthe hydrocarbon formation is underreamed to a radius of about two inchesgreater than the outside diameter of the protective casing string. Theunderreaming is accomplished using one of the :above-mentionedcirculating fluids. A perforated liner `66 is installed opposite thehydrocarbon-'bearing formation interval. The liner is preferablyequipped with a liner hanger device comprising lugs 67 and packing means68. Alternatively the perforated liner may be simply set down on thebottom of the well and left uncentralized or centralized with an adapterhaving fluid passages rather than hung on the protective casing stringas shown in FIGURE 2. A port Collar arrangement 70 is preferablyprovided in the upper portion of the liner where a hanger is employed.The port collar can be moved to a closed position after the charcoal isin place -behind the liner.

Coarse, particulate charcoal is then packed in the annulus between theperforated liner and the hydrocarbon formation over the entirehydrocarbon formation interval. The charcoal is 'brought into intimate-contact with the hydrocarbon-bearing formation. The charcoal iscirculated into the annulus through the ports in the gravel packingcross-over tool or around the liner top before setting an adapterutilizing one of the above-mentioned circulating fluids. The fluidreturns are either taken to the surface via the well bore annulus 40 ordisplaced directly into the hydrocarbon-bearing formation. After thecharcoal has been placed, the gravel packing tool, if one is used, isretrieved from the well and the inside of the perforated liner iscleaned out to total depth.

An inert atmosphere is established in the well by circulating an inertgas such as nitrogen or carbon dioxide into the well bore to fill thewell from total depth to the surface. A pyrophoric material capable ofcausing the charcoal to autoignite is then introduced into the well borethrough a suitable lubricator and placed on and in the uppermostportions of the charcoal in the linerormation annulus. Suitablepyrophoric materials include tri-ethyl-borane, yellow phosphorus, carbondisulfide and nitric acid. Other suitable materials may be used.

Referring to FIGURES 4 and 5, a suitable technique for placing thepyrophoric material on the upper portion of the charcoal is shown. Withthe well closed in, a bailer 75 having pack-off foot 76 is loweredthrough a lubricator by suitable means such as wireline 78 to a positionon top of the upper portion of the perforated liner. Inert gas iscontained in the bailer under pressure to blow the pyrophoric materialwhich is usually a liquid, out of the bailer 75 and into the smallannular space between the liner and the protective casing string. Thedischarge is accomplished by the foot 76 opening a discharge valveindicated by the numeral 81 or Aby the pintle 77, being constructed inthe form of a punch rather than tted with a valve, puncturing a sheardisc located in place of the discharge valve. The liquid runs throughthe spaces 79 in the liner supporting means `and down into the upperportion of the charcoal pack. The bailer is then removed from the wellwhile maintaining the inert atmosphere in the well.

The wellhead is closed in and oxygen-containing gas is pumped into thewell at a rate regulated to displace the inert atmosphere in the welland to kautoignite the pyrophoric material to initiate combustion of thecharcoal in the liner-formation annulus. Itis of lprimary importance tohave the oxygen-containing gas which is usually air, flow through theperforations in the slotted liner and thence into the charcoal pack.Sufficient oxygen-containing gas is injected to burn the charcoal at asufficient rate to ignite the hydrocarbons in the formation with whichit is in contact but at an insufficient level to generate heat requiredto fuse the formation. Generally the temperature at the liner is keptbelow about 700 F. The combustion of the charcoal is advanced from thetop of the pack to the bottom by the continued injection ofoxygen-containing gas. A sufficient amount of oxygen-containing gas isinjected into the well to provide for continual passage of gas throughthe perforations in the liner. In this manner the temperature of theliner is maintained at a safe level by the relatively cool gas passingtherethrough. The air rate required to effect proper combustion isregulated by the length of interval being processed, the radialthickness of the charcoal or coke bed7 the rate of burning of the beddesired and the amount of air by-passing the ignited bed.

As the charcoal is burned the temperature of the hydrocarbons in theformation will be elevated to a ternperature suicient to createcombustion in the hydrocarbon-bearing formation. The ashes created bycombust-ion of the charcoal will tend to be carried linto theparticularly permeable portions of the hydrocarbon formation and willassist in partially plugging the highly permeable portions to therebyassist in establishing a relatively uniform injection profile across thehydrocarbonbearing interval. If the injection profile can be maintainedon a relatively stable basis across the entire interval, the chances ofobtaining uniform ignition of the hydrocarbons across the interval isgreatly improved. After the ignition of the hydrocarbons in theformation has been established, combustion is moved out into theformation away from the well bore. The rate of injection ofoxygencontaining gas can then be adjusted to a rate suitable foraccomplishing the purposes of the UGC project.

Although only embodiments of the invention have been described andillustrated, the invention is not to be limited to only such embodimentsbut rather `it is intended that the invention embrace all equivalentsfalling within the scope of the appended claims:

1. A method of igniting an underground petroleumbearing formationcomprising the steps of drilling a well from the earths surface topenetrate at least a portion of an underground petroleum-bearingformation, installing a perforated linear in the well opposite the saidformation in a manner to provide an annular chamber be tween the welland the outside of said perforated liner, packing the said annularchamber with an ignitable material, establishing an inert gas atmospherein the well, introducing a pyrophoric material in said well and into atleastthe. upper portion of the ignitable material in said annularchamber, replacing the inert atmosphere in the well with anoxygen-containing gas, continuing to inject oxygen-containing gas iintothe well and out through the perforations in said perforated liner intothe pack of ignitable material to establish combustion in the ignitablematerial and continuing to inject an oxygen-containing gas into the saidwell and through said pack at a sueient rate to ignite the hydrocarbonsin said petroleum-bearing formation.

2. A method of igniting an underground petroleumbearing formationcomprising the steps of drilling a well from the earths surface topenetrate at least a portion of an underground petroleum-bearingformation, enlarging the diameter of the portion of the well penetratingthe said formation, installing a perforated liner in the well oppositethe said formation in a manner to provide an annular chamber between thewell and the outside of said perforated liner, packing the said annularchamber with charcoal, establishing an inert gas atmosphere in the Well,introducing a pyrophoric material in said well and into at least theupper portion of the charcoal in said annular chamber, replacing theinert atmosphere in the well with an oxygen-containing gas vandcontinuing to inject oxygencontaining gas into the well and out throughthe perforations in said perforated liner into the charcoal pack toestablish combustion in the charcoal, and continuing to inject anoxygen-containing gas into the said well and through said pack at asucient rate to ignite the hydrocarbons in said petroleum-bearingformation.

CHARLES References Cited UNITED STATES PATENTS 10/1961 Marx et al.166-39 X 11/1961 Gerner 166-39 X 3/1963 Harlan 166-39 5/1964 Wyllie166-39 X 12/1965 Hujsak 166-38 E. OCONNELL, Primary Examiner.

I. A. CALVERT, Assistant Examiner.

U.S. Cl. X.R.

